Recovery of raw materials from magnetic recording media

ABSTRACT

Magnetic powder and substrate material are separately recovered from finely chopped wastes of magnetic recording media consisting of a polymeric substrate and a magnetic layer present thereon in which finely divided magnetic powder is dispersed in crosslinked or uncrosslinked polymeric binder by treating the finely chopped wastes of magnetic recording media in a solution consisting of the potassium salt of a polyunsaturated fatty acid, or a biodegradable cleaning agent comprising phosphates, surfactants and a complexing agent, and one or more organic solvents or water while being subjected to mechanical action, and separately removing the magnetic powder from the substrate material by washing or sedimentation or in a magnetic separator.

The invention relates to a process for recovering raw materials fromfinely chopped wastes of magnetic recording media, consisting of apolymeric substrate and a magnetic layer present thereon, in whichfinely divided magnetic powder is dispersed in crosslinked oruncrosslinked polymeric binder, the magnetic powder and the substratematerial being recovered by treatment in an alkaline medium.

In recent years, the rapid growth of the information industry hasresulted in extensive consumption of large amounts of magnetic storagemedia, such as computer tapes, audio tapes, video tapes and diskettes.In particular, magnetic tapes and diskettes which have, for example,polyethylene terephthalate as the substrate have been produced ingrowing amounts in recent years, owing to their excellent magnetic andmechanical properties. In general, residues and wastes of such storagemedia occur in large amounts in the production and during use by the endusers. At present, such wastes are disposed of by depositing them withthe domestic waste in sanitary landfills or incinerating them inincineration furnaces. From the point of view of waste reduction and therecovery of useful materials, full utilization of such wastes is anoutstanding requirement.

A process of the generic type stated at the outset is disclosed inGerman Offenlegungsschrift DOS 3,341,608. According to this publication,the magnetic tape wastes are finely shredded, after which the magneticlayer and the substrate are delaminated in aqueous alkaline solution andthe magnetic powder is separated from the substrate by stirring at highspeed. This process requires a very complicated bulky apparatus.

Further processes which are based on separation of the magnetic layerfrom the substrate by treatment with a base are described in JapaneseApplications 112 979 (1978), 006 985 (1979), 070 404 (1978), 092 879(1978) and 167 601 (1987) and Korean Application 89/03614. JapaneseApplications 313 707 (1988), 112 413 (1989) and 146 624 (1982) describeseparation by treatment with an acid. Japanese Application 054 050(1983) describes the use of a solvent mixture comprising phenol andtetrachloroethane for delamination of the magnetic layer.

U.S. Pat. No. 5,246,503 discloses a delamination solution for coatingswhich consists of organic solvent, water, thickener and wetting agent,but where in addition the coating has to be removed mechanically byscratching.

If it is intended to delaminate the magnetic layer and the substrate andthe aim is to recover the useful materials, in particular the magneticpowder and the polyethylene terephthalate, the PET film should as far aspossible not be chemically degraded or attacked. If, on the other hand,polyurethanes crosslinked in the magnetic layer, are used as binders asdescribed, for example, in European Patent 0,099,533, the processesdescribed above are for the most part unsuccessful or giveunsatisfactory results with regard to separation, delamination andrecovery.

German Application P 43 30 839.9 discloses a process for recovering rawmaterials from magnetic recording media, in which these raw materials infinely chopped form are treated in organic solvents, an acid which issoluble therein and alcohols or thioalcohols and, if required,surfactants at elevated temperatures, the magnetic layer delaminated inthis manner being separated from the substrate by a washing process, andthereafter both the finely shred substrate wastes and the magneticpowder being dried. That feature of this process which is essential forthe invention is that the ester groups of the polyurethane binder arecleaved by hydrolysis by the stated treatment medium, whereas at thesame time the ester groups of the polyethylene terephthalate substrateare not chemically destroyed. It has been found that it is difficult inthis process to fulfill these boundary conditions; furthermore, thefinely shred wastes must be treated for many hours in order to achievecomplete separation.

It is an object of the present invention to provide a process of thegeneric type stated at the outset, in which the magnetic layer isdelaminated from the PET substrate film without the latter beingchemically cleaved. It is a further object of the present invention tofind reaction conditions under which only a short reaction time isrequired for delamination and separation of magnetic powder andpolyethylene terephthalate substrate film.

We have found, completely surprisingly, that this object is achieved bytreating the abovementioned magnetic recording media in finely choppedform in an alkaline medium, consisting of the potassium salt of apolyunsaturated fatty acid, one or more organic solvents and, ifrequired, water and, if required, a suitable catalyst, while stirringand at elevated temperatures.

We have found that this object is furthermore achieved by an alkalinecomposition in which a biodegradable cleaning agent consisting ofspecific phosphates, surfactants and completing agents, which has a pHof >10, is used instead of the potassium salt of a polyunsaturated fattyacid. As described in more detail further below, the further treatmentis carried out essentially as in the abovementioned German Application P43 30 889.9, so that the useful materials thus recovered, ie. thepolymeric substrate material and the magnetic powder can be fed tofurther processing and use steps in the manner customary for them.

The novel process and the apparatuses required for carrying out theprocess and reactants and boundary conditions are described in moredetail below.

The polymeric substrate material which may be used in the novel processmay consist of polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate, cellulose, polyamide, polyimide, vinylpolymers or other polymers. These substrates may have beencorona-treated or provided with a layer of adhesive-forming components,as disclosed in the prior art.

The binders used in the prior art magnetic layer are usuallypolyurethanes, which in general are synthesized from diisocyanates,polyesterols as flexible segments, low molecular weight alcohols andamino alcohols having a relatively high functionality and short-chaindiols as chain extenders. However, polycarbonate/polyurethanes andpolyurethanes composed of other segments are also known.

The polymeric binder may, however, also be a mixture of polyurethanewith copolymers of vinyl chloride, vinyl acetate and vinyl alcohol,copolymers of vinylidene chloride and acrylonitrile, polyvinyl acetals,for example polyvinyl formal, or cellulose derivatives, such asnitrocellulose, and phenoxy resins and epoxy resins.

The stated binders may be present as an uncrosslinked or crosslinkedmatrix, in general polyfunctional isocyanates, if necessary supported bya crosslinking catalyst, acting as crosslinking agents.

Suitable magnetic powders are the conventional pigments used inproducing the magnetic recording media, such as γ-Fe₂ O₃, Fe₃ O₄,berthollide iron oxides FeO_(x), where 1.33<x<1.50, CrO₂, metal powdersor metal alloy powders and mixtures thereof.

The alkaline treatment medium consists of the potassium salts ofpolyunsaturated fatty acids (trivial name soft soap), one or moreorganic solvents and, if required, water and a catalyst.

The abovementioned biodegradable cleaning agent, consisting of specificphosphates, surfactants and complexing agents, is known under the tradename Mukasol®.

The fact that it is not the high pH of >10 alone which is critical forcomplete and rapid delamination of the magnetic layer, as is known fromthe cited prior art, is shown by Comparative Sample 3 of Example 1, inwhich a composition consisting of Newamatic®, a washing agent having apH of 12 and the stated solvents was used. Here, no delamination wasobserved in the course of 1 hour at boiling point.

If, in the stated composition, the potassium salt of the polyunsaturatedfatty acid is replaced by, for example, the sodium salt of a saturatedfatty acid (trivial name curd soap), delamination is more difficult orimpossible.

Suitable organic solvents are N-methylpyrrolidone, dimethylformamide,dimethyl sulfoxide, methyl ethyl ketone, dibutyl ether, tetrahydrofuran,1,4-dioxane, acetone, cyclohexanone, toluene, xylene, chloroform,methylene chloride, trichloroethylene, isopropanol, methanol, ethanol,butanone and tetrachloroethane and in particular mixtures thereof andmixtures with water.

The basic catalyst sodium methylate, potassium tert-butylate, sodiumoxaloacetate or dimethylaminopyridine has proven a particularly usefulcatalyst, but o-butyl titanate or simply NaOH is also suitable as anadditive.

In addition, surfactants may also be used, in a combination with theabovementioned components, for delamination of the magnetic layer.Examples of suitable surfactants are higher fatty acids or oxo alcoholswhich have been alkoxylated with ethylene oxide, propylene oxide orbutylene oxide so that they are soluble or dispersible in the solventsystem, for example C-13 or C-15 oxo alcohol ethoxylated with 3 units ofethylene oxide.

As stated above, the composition described above operates in thealkaline range from pH 9 to pH 13, preferably from pH 10 to pH 12.

To carry out the novel process, the magnetic recording medium is cutinto small or medium-sized pieces and the stated washing solution isadded. This may advantageously be effected in a reactor space, as shownin the FIGURE.

In the upper part (1) of the reactor space, the film shreds (2) areintroduced and are mixed thoroughly by means of the stirrer (3) havingthe paddles (4) with the treatment liquid (5) present in the reactorspace. The reaction temperature is close to the boiling point, ie. from60 to 95° C., preferably from 85 to 90° C. The addition of small steelpins or grinding balls composed of steel or ceramic in order to achieveoptimum friction against the magnetic layer is also advantageous.

After a few minutes, the delamination process is complete. Separation ofthe magnetic powder from the substrate film may be effected, as shown inthe Figure, by arranging, between the upper part (1) and the lower part(7) of the reactor space, a perforated plate (6) which is so fine-meshedthat it is permeable only for the magnetic powder removed but not forthe film shreds of the magnetic recording medium. Consequently, themagnetic powder removed collects in the lower reactor space (7) owing togravitational force and remains there. No fluidization takes place sincethe action of the stirrer in the lower reactor space is negligible owingto the perforated plate. The lower reactor space may additionally bedivided by a plurality of partitions (8).

The reaction time is dependent on the composition of the washingsolution used and on the treatment temperature and is not more than onehour. In order to reduce the reaction time, the action of ultrasonics isalso preferred in addition to the thorough stirring of the finelychopped magnetic tape wastes.

The magnetic powder removed can then be separated completely from thefilm shreds by washing with the solvent mixture used or with puresolvents. The addition of suitable flocculants, such as copolymers basedon acrylamide, or magnetic separators known from the stated prior art,such as permanent magnets or magnets energized by alternating current,is advantageous.

The film shreds can then be dried in an air stream or under reducedpressure and then put to further use. In carrying out the novel process,it has been found that the substrate shreds have essentially unchangedproperties compared with substrates used for the first time.

The magnetic sludge, consisting of solvents and magnetic powder, isfreed from the solvent and the magnetic powder is dried under reducedpressure. It can be processed by existing technologies to give magneticpigments again. It has also been found that the treatment solutionsdescribed are suitable for reuse, ie. do not have to be destroyed aftereach delamination process.

EXAMPLE 1

A magnetic dispersion having the composition

    ______________________________________                                                           Parts by weight                                            ______________________________________                                        Finely divided acicular CrO.sub.2                                                                  11                                                       High molecular weight polyurethane                                                                 1.6                                                      Vinyl copolymer VAGH 0.6                                                      Lubricant            0.04                                                     Dispersant           0.2                                                      crosslinking agent, diisocyanate                                                                   0.4                                                      Solvent              23                                                       ______________________________________                                    

is cast on a nonmagnetic 15 μm thick polyethylene terephthalatesubstrate by means of a conventional extrusion coater to give a layerwhich is 3.5 μm thick when dry, and said layer is then dried, calenderedand subjected to aftertreatment at elevated temperatures. For theproduction of video tape, the coated films are slit into half inchwidths (1.27 cm) in the longitudinal direction. The magnetic recordingmedium thus produced is cut into pieces from 5 to 30 cm long andsubjected to the following treatment according to Table 1 in order torecover substrate material and magnetic powder by the novel process.

The film pieces are initially taken in a round-bottom flask and thenovel solvent mixture is added. The amounts used are shown in the Table.The mixture is heated while stirring. After the time shown in the Table,within which the coating has been removed, the mixture is allowed tocool and is filtered through a fine-meshed sieve. Washing is carried outwith tetrahydrofuran (THF) and water, and the remaining film pieces aredried in a drying oven. The magnetic powder washed away is freed fromthe solvent and dried under reduced pressure.

The stated washing solution has a pH of 12 in each case. The reactiontemperature corresponded to the boiling point of the washing solution.This washing solution can be reused several times, which is anadditional advantage.

                                      TABLE 1                                     __________________________________________________________________________                                            Delamination                          Sample    Solvent       Catalyst Cleaning agent                                                                       time (min)                            __________________________________________________________________________    1         65 dioxane, 32 water   3 S    28                                    2         62 dioxane, 32 water   6 S    25                                    3         70 dioxane, 15 water   15 S   20                                    4         65 dioxane, 32 methanol                                                                              3 S    7                                     5         65 xylene, 32 methanol 3 S    22                                    6         65 butanone, 32 methanol                                                                             3 S    18                                    7         65 tetrahydrofuran, 32 methanol                                                                      3 S    8                                     8         65 tetrahydrofuran, 32 ethanol                                                                       3 S    17                                    9         81 tetrahydrofuran, 16 methanol                                                                      1 S    5                                     10        81 tetrahydrofuran, 16 methanol                                                                      0.5 S  8                                     11        81 tetrahydrofuran, 16 methanol                                                             0.05 NaOCH.sub.3                                                                       3 S    2.5                                   12        81 tetrahydrofuran, 16 methanol                                                             0.05 o-butyl titanate                                                                  3 S    2.5                                   13        81 tetrahydrofuran, 16 methanol                                                                      3 M    10                                    Comparative Sample 1                                                                    65 tetrahydrofuran, 32 water                                                                         3 C    --                                    Comparative Sample 2                                                                    65 tetrahydrofuran, 32 methanol                                                                      3 C    --                                    Comparative Sample 3                                                                    81 dioxane, 16 water   3 N    --                                    __________________________________________________________________________     All data in grams; S = soft soap; C = curd soap; M = Mukasol ®; N =       Newamatic                                                                

EXAMPLE 2 (ALL DATA IN PARTS BY WEIGHT)

In each case three roughly 3 cm long strips of commercial half inch(1.27 cm) wide video tapes were treated in a mixture of 58 parts oftetrahydrofuran, 12 parts of methanol and 1.2 parts of soft soap at theboil. The following results were obtained.

                  TABLE 2                                                         ______________________________________                                        Video tape type  Delamination time                                            ______________________________________                                        RELAX HGX E240   30 minutes                                                   PDM EHG E240      5 minutes                                                   Scotch S-VHS     10 minutes                                                   Scotch EG+ E180  10 minutes                                                   Unilever SUM HG E180                                                                           10 minutes                                                   TDK E-HG          5 minutes                                                   JVC SX 195       10 minutes                                                   Kendo SHG E195   10 minutes                                                   Sony V            3 minutes                                                   Maxell HGX Black E180                                                                           9 minutes                                                   Maxell HGX Black prof.                                                                          7 minutes                                                   Maxell XR-S S-VHS                                                                              10 minutes                                                   Maxell VX 195    10 minutes                                                   Fuji HQ E195     30 minutes                                                   Fuji S-HG E180   30 minutes                                                   Kodak HS 240      7 minutes                                                   ______________________________________                                    

EXAMPLE 3

In each case three roughly 30 mm long 3.81 mm wide strips of commercialaudio cassette tapes were treated in a mixture as in Example 2, at theboil. The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Tape type         Delamination time                                           ______________________________________                                        Sony              2 minutes                                                   UXS Type II High CrO.sub.2                                                                      2 minutes                                                   UX Pro90 LEC II Type II                                                                         2 minutes                                                   HF 90 Type I      2 minutes                                                   Esprit II         2 minutes                                                   Fuji GT-IIx90 Type II                                                                           2 minutes                                                   Fuji JP-IIx90 Double Coating                                                                    3 minutes                                                   TDK D 60 Type I   5 minutes                                                   TDK SF 60 Type II 2 minutes                                                   TDK SA-X Type II  2 minutes                                                   TDK SA90 High Position                                                                          5 minutes                                                   Maxell XL II 90   5 minutes                                                   Maxell XL II S 90 30 minutes                                                  Maxell UR-F 90    3 minutes                                                   Maxell UR 90      4 minutes                                                   ______________________________________                                    

EXAMPLE 4

A commercial video tape was treated in a mixture according to Example 2at the boil, but the amount of soft soap was changed and water wasadded. The results are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                        Soft soap     Water   Delamination time                                       ______________________________________                                        1.2 parts     --      15 minutes                                              1.2 parts     0.2     23 minutes                                                6 parts     0.2     15 minutes                                              1.2 parts     0.6     26 minutes                                              ______________________________________                                    

EXAMPLE 5

In each case 5 cm² of finely chopped, commercial floppy disk materialcoated on both sides were treated in a mixture as in Example 2 at theboil. The results are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                        Diskette type   Delamination time                                             ______________________________________                                        RPS 3.5"        2 minutes                                                     Teijin 3.5"     5 minutes                                                     Nippon-Columbia 3.5"                                                                          4 minutes                                                     BASF 5.25"      4 minutes                                                     BASF 3.5"       4 minutes                                                     ______________________________________                                    

EXAMPLE 6

In each case 5 cm² of finely chopped, commercial half inch wide (1.27cm) computer tape which was intended for the type 3480 mono reelcassette in which the magnetic layer was cast on a corona-treated PETfilm were treated in a mixture as in Example 2 at the boil, with variousadditives, the results shown in Table 6 being obtained.

                  TABLE 6                                                         ______________________________________                                                                Delamination time                                     Additive (parts)  pH    (min)                                                 ______________________________________                                        0.01 of NaOH      9     9                                                     1.2 of potassium tert-butylate                                                                  9     30                                                    0.6 of sodium oxaloacetate                                                                      11    3                                                     1.2 of dimethylaminopyridine                                                                    11    30                                                    ______________________________________                                    

EXAMPLE 7

Results similar to those in Example 6 were obtained when the procedurewas as in Example 6 except that the magnetic layer had been cast on aPET substrate provided with a 0.2 μm thick layer of adhesive-formingcomponents.

EXAMPLE 8

Results similar to those in Example 6 were obtained when, in the solventmixture, the 12 parts of methanol were replaced by equal amounts ofethanol, i-propanol or toluene.

EXAMPLE 9

This mixture was treated as in Example 6, except that 12 parts of softsoap were used. The delamination time was then 30 minutes (when furtheradditives from Table 6 were absent).

EXAMPLE 10

The procedure was as in Example 6, except that 58 parts of dioxane, 12parts of ethanol and 12 parts of soft soap were used as the treatmentsolution. The delamination time was 30 minutes.

If the Examples are considered together with the Comparative Examples,it is evident that, by a suitable choice of the treatment solution andthe treatment parameters, complete delamination of the magnetic layer isachievable in a short treatment time without damaging the polyethyleneterephthalate substrate.

We claim:
 1. A process for separately recovering the magnetic powder andthe substrate material from finely chopped wastes of magnetic recordingmedia, consisting of a polymeric substrate and a magnetic layer presentthereon, in which finely divided magnetic powder is dispersed incrosslinked or uncrosslinked polymeric binder, whereinthe finely choppedwaste of magnetic recording media is treated in a solution consistingofa) the potassium salt of a polyunsaturated fatty acid, or b) abiodegradable cleaning agent comprising phosphates, surfactants and acomplexing agent, and one or more organic solvents or water while beingsubjected to mechanical action, andthe magnetic powder removed is thenseparated from the substrate material by washing or sedimentation or ina magnetic separator.
 2. The process of claim 1, which is carried out inthe presence of a catalyst.
 3. The process of claim 1, wherein theorganic solvent is selected from the group consisting of dioxane,N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, dibutylether, methyl ethyl ketone, tetrahydrofurane, 1,4-dioxane, acetone,cyclohexane, toluene, xylene, isopropanol, methanol, ethanol, butanoneor a mixture thereof.
 4. The process of claim 2, wherein the catalyst isselected from the group consisting of sodium methylate, potassiumtert-butylate, sodium oxaloacetate, dimethylaminopyridine or o-butyltitanate.
 5. The process of claim 1, which is carried out at a pH offrom 10 to 12, at from 60 to 95° C. while stirring and/or with theaction of ultrasonics.
 6. The process of claim 1 which is carried out inthe presence of surfactants, which in the case when there is abiodegradable cleaning agent, are in addition to the surfactants in thebiodegradable cleaning agent.
 7. The process of claim 1, wherein thesurfactants are higher fatty acids or oxo alcohols which have beenalkoxylated with ethylene oxide, propylene oxide or butylene oxide.